Spade drills have become increasingly popular because of the ability to replace the spade drill blades when they become dull rather than the entire blade and holder as is required with conventional twist drills. Spade drills have a major disadvantage; they are difficult to center when initially entering the work piece and they can vibrate or shake in the work piece because of voids, uneven hardness, or deflection from pressure of the work piece material causing the cut or bore to drift. Because of this, spade drills are not the drill of choice for high tolerance work. This is unfortunate because spade drills cut fast and are inexpensive compared to twist drills in larger sizes.
It is an object of the present invention to provide a self centering spade drill which needs no center drill hole to align the drill.
A further object of this invention is to provide an improved spade drill which is tighter, more stable, and more precise than conventional spade drills.
A further object of the present invention is to provide an improved spade drill which has more cutting surfaces and thus can provide for faster cutting into the work piece and easier drilling with less pressure and less heat production.
It is a further object of the present invention to provide a drill holder for the improved self centering spade drill which will securely and tightly hold the drill in place and which permits the drill to be fit on conventional drilling machines and computer numerical control (CNC) machining centers.
A further object of the present invention is to provide an adaptor for securing the improved self centering spade drill onto a conventional holder for spade drill blades.